Various chemical treatments exist for glass-type surfaces such as glass fibers to aid in their processability and applications. Before bundling the filaments together after formation, a coating composition or sizing composition is applied to at least a portion of the surface of the individual filaments to protect them from abrasion and to assist in processing. As used herein, the terms “sizing composition,” “sizing,” “binder composition,” “binder,” or “size” refer to a coating composition applied to the filaments immediately after forming. Sizing compositions can provide protection through subsequent processing steps, such as those where the fibers pass by contact points as in the winding of the fibers and strands onto a forming package, drying the aqueous-based or solvent-based sizing composition to remove the water or solvent, twisting from one package to a bobbin, beaming to place the yarn onto very large packages ordinarily used as the warp in a fabric, chopping in a wet or dry condition, roving into larger bundles or groups of strands, unwinding for use as a reinforcement, weaving, and other downstream processes.
In addition, sizing compositions can play a dual role when placed on fibers that reinforce polymeric matrices in the production of fiber-reinforced plastics or in the reinforcement of other materials. In the reinforcement of polymeric matrices, the sizing composition can provide protection and also can provide compatibility between the fiber and the matrix polymer or resin. For instance, glass fibers in the forms of both woven and nonwoven fabrics and mats and rovings and chopped strands have been used with resins, such as thermosetting and thermoplastic resins, for impregnation by, encapsulation by, or reinforcement of the resin. In such applications, it may be desirable to maximize the compatibility between the surface and the polymeric resin while also improving the ease of processability and manufacturability.
Glass fibers are sometimes coated with additional compositions after being coated with a sizing composition and prior to use as a reinforcement. For example, glass fibers are sometimes coated with a vinyl addition polymer such as polyvinyl chloride (PVC) to protect the glass fibers. For example, glass fibers can be used to reinforce a cementitious material. However, certain glass fibers (e.g., E-glass fibers) can deteriorate in the alkaline environment of a cementitious material. Thus, the glass fibers can be coated with PVC to minimize the damage which might result from reaction with an alkaline cementitious material.
When secondary coatings, such as PVC, are applied to glass fibers, the sizing composition can provide compatibility between the fiber and the secondary coating. A sizing composition can also provide strength to the glass fibers. Thus, the selection of a sizing composition for glass fibers is important to the performance of the glass fibers.
As mentioned above, glass fibers can be used as reinforcement for cementitious materials. An example of such a product is “cement board,” in which a woven mesh of fiber glass strands is used to reinforce a cementitious material. In such products, the fiber glass strands are at least partially coated with a PVC plastisol prior to placement in the cementitious material. Cement board can be used in a number of ways, but is often used as a backerboard for ceramic tiles or bathroom fixtures.
An important property of fiber glass strands used in cement board is tensile strength. As used herein in connection with a fiber glass strand, whether coated with PVC or not, “tensile strength” refers to the amount of force required to break the strand.
It would be desirable to provide a fiber glass product coated with a sizing composition that has a number of desirable properties, including compatibility with PVC or other secondary coatings, a desirable tensile strength, a desirable strength when coated with PVC or another secondary coating, a desirable strength when used to reinforce a cementitious material, and/or other properties.